The present work developed an experimental and simulation study to evaluate the influence of some operational conditions and mold design on the efficiency of an injection process used to produce polystyrene parts. The software SolidWorks Plastic was used to simulate the injection process and assess the performance of the mold considering the absence and the presence of venting. Experimental results obtained by varying the injection pressure, injection temperature as well as the mold temperature were used to validate the simulation data generated considering both mold designs. The findings revealed air entrapment at the end of the mold cavity and low process efficiency when the mold was operated with no venting, regardless the processing conditions. Simulation results indicated a remarkable increase of the process efficiency when vents were included on the parting line of the mold. In addition, the range of processing conditions which led to the highest process efficiency was virtually identified and tested in the real modified mold (with venting system). The findings revealed that the injection cycle time reduced in approximately 35% and the waste generation diminished from 65% to less than 1% when venting was included in the mold design and the optimal operational conditions were used.